House amplifier with return path gating

ABSTRACT

In a traditional HFC plant, the return path signals originating from cable modems, eMTAs, and settop boxes are transmitted in the 5-42 MHz range (other countries use frequencies such as 5-30 MHz, 5-55 MHz, and 5-65 MHz). These signals with entry points at any RF connection point in the home are combined by RF combiners at the side of the house. Furthermore, RF return path signals from multiple homes are combined by RF taps into a coaxial cable TV plant, and transmitted back to a hub or headend either in RF or thru a fiber optic network. 
     In addition to combining all RF signals, the return path system combines all the ingress noise from all the RF connection points, which has an adverse impact on signal quality. This invention takes advantage of the burst nature of RF return path signals to insert an automatic gating function into the return signal path of a house amplifier so that the return signal path is shut off or attenuated when no RF return signal is present. This has the advantage of eliminating completely any ingress noise contribution when the cable modem, eMTA, or settop box are not actively transmitting, thereby improving overall coaxial cable plant&#39;s signal quality.

This application claims priority of U.S. Provisional Application No. 61/074,898 filed on Jun. 23, 2008 under 35 U.S.C. §19(e), the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

a) Field of the Invention

The present invention relates to video, voice, and data communications in a CATV (cable television) network. More particularly, the present invention is capable of improving return path signal quality of the traditional HFC (hybrid fiber coax) network architectures used by CATV service providers, consequently allowing for longer transmission distances, higher signal modulation formats in the order of higher order of M-QAMs, and higher network reliability.

b) Description of the Prior Art

Communications networks today are required to provide higher and higher bandwidth as subscriber bandwidth demands grow due especially to internet applications such as file sharing, video conferencing, ecommerce, consumer video production and subsequent posting to sites such as Youtube, etc. While many ILECs (incumbent local exchange carriers) and CLECs (competitive local exchange carriers) have taken the approach of completely rebuilding their networks using fiber-based technologies such as GPON, this has resulted in both expensive plant upgrades and equipment replacement. Existing copper plants are replaced by fiber builds. DSL modems are replaced with GPON ONTs and IP settop boxes are deployed to consumer homes, while complete digital headends have to be built.

CATV operators have in the past 20 years progressed from being entertainment providers to being also broadband providers and then voice service providers. However, CATV operators face the same bandwidth demand growth. Different solutions have been applied, which include higher modulation schemes in both forward path (downstream) and return path (upstream) signals. Currently many CATV operators use 256 QAM modulation for downstream signals, and are actively migrating from 16 QAM to 64 QAM for upstream return path signals.

As higher levels of modulation are used, the required signal to noise ratio (signal quality) increases. This means that the good signals originating from cable modems, eMTA and cable settop boxes must be at a sufficient power level above unwanted interfering noise to ensure good data transmission quality. Furthermore, the popular use of eMTAs for VoIP service means that data communications over the HFC network need to progress from previous a best-effort service to a guaranteed level to ensure quality of voice communications.

In an HFC plant, most of the unwanted noise signals enter the HFC plant from the home. This can be caused by any combination of unterminated coaxial F-ports; bad shielding of televisions, VCRs, or cable boxes; and low quality RF amplifiers with either bad shielding, self oscillations, return loss, or distortions which all combine to allow ingress of noise.

HFC networks employ the DOCSIS standard for bi-directional data transmission. The DOCSIS cable modem and eMTA in the home transmits return path data as needed in bursts. This means that when not actively transmitting data, the cable modem is inactive. Cable settop boxes also use a burst mode transmission pattern, sending return path signals only when the home user orders a particular movie from the VOD or PPV service. However, despite of the burst nature of return path signals, present HFC plant design provides for a return signal path that is always open, so that ingress noise is transmitted even though no active transmission is taking place.

Since ingress noise from all the homes are added together because of the noise funneling effect of the HFC plant (FIG. 1), this noise funneling effectively sets the limit on the number of homes per node, as well as the highest modulation level that can be used. In order to reduce ingress noise so that higher modulation levels can be used, CATV operators have to reduce node sizes, which require expensive HFC plant upgrades consisting of new optical fiber deployment and capital equipment investment.

SUMMARY OF THE INVENTION

This invention eliminates the problem of ingress noise addition in the HFC coaxial plant by implementing a solution as shown in FIG. 2. In this implementation, an RF gate in the form of an RF switch or variable attenuator is added to the return signal path portion of a house amplifier so that when no RF signal is present, the RF signal path is switched off and no ingress noise contribution can enter the HFC coaxial plant from the home to which the house amplifier is connected.

In previous implementations of devices for troubleshooting return path ingress noise issues, the RF gate mentioned above is turned on or off by a user through remote signaling. This approach can only be used for troubleshooting, where attempt is made to identify sources of ingress noise. This approach has limitations in that a) only identification of the source of noise is made, but no improvement is made through this method; b) accurate detection or identification of the source of noise may not be possible due to the transient nature of certain ingress noise sources; c) direct manipulation is required of a human operator; d) network availability is interrupted; and e) repair is not always possible especially when ingress noise originates in a customer's home.

This invention uses an automatic detection circuit (FIG. 3) consisting of a high speed RF detector, a amplifier, and a timing circuit to detect the presence of RF return path signals from a cable modem, eMTA, or settop box. Once the presence of the RF signal above a certain signal threshold level is detected, the detection circuit with turn on the RF gate, allowing RF signal to pass through. The timing circuit enables a fast turn on of the RF gate, with a turn off delay to ensure all signals pass through before the RF gate is shut off.

To enable a further understanding of the said objectives and the technological methods of the invention herein, the brief description of the drawings below is followed by the detailed description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1—Return path noise funneling. In a traditional HFC plant, RF signals are combined, which results in ingress noise from all subscriber homes to be added together, which negatively impacts the SNR (signal to noise ratio) of the system.

FIG. 2—House amplifier with return path gating. Return signal path of a house amplifier is gated so that ingress noise is blocked when RF return transmission is not active, so that no noise contribution is received from inactive return path.

FIG. 3—Automatic detection circuit. Automatic detection and control logic output to automatically turn on RF gate when return RF signal is present, and automatically turn off the RF gate when no return RF signal is present.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention may be embodied in a house amplifier. The house amplifier may be installed on the side of the house, in a garage or basement. The said house amplifier may be called by other names such as drop amplifier, RF amplifier, and CATV amplifier. The house amplifier can consist of any number of output ports (commonly from single port devices to as many as 24 output ports), active or passive forward path amplification, and active or passive return path amplification.

FIG. 2 shows a functional block diagram illustrating an exemplary house amplifier. The exemplary house amplifier comprises of a pair of diplex filters to separate forward signal path from return signal path, optional RF amplifiers for forward and return signal path, RF sampling circuit, automatic detection circuit, and RF gate.

When a return path RF signal enters the house amplifier through the Return Input port shown in FIG. 2, it is routed by the diplex filter to the Return Signal Path. The Sampling Circuit further routes a portion of this signal to the Automatic Detection Circuit of FIG. 3. The RF Detector shown in FIG. 3 demodulates the RF signal and outputs the demodulated signal to provide a voltage output level corresponding to the RF signal power of the source signal. The amplifier in FIG. 3 further amplifies this voltage output level so that on or off conditions can be detected using standard logic components. Either CMOS or TTL logic can be used depending on the gain of the amplifier, which can be implemented simply using operational amplifiers and feedback gain control. The Timing Circuit shown in FIG. 3 allows a fast on, slow off control of the RF gate to prevent data loss.

The RF Gate shown in FIG. 2 can be implemented through the use of a) RF switch for complete on/off control, or b) voltage controlled attenuator for full on, partial off control.

It is of course to be understood that the embodiments described herein is merely illustrative of the principles of the invention and that a wide variety of modifications thereto may be effected by persons skilled in the art without departing from the spirit and scope of the invention as set forth in the following claims. 

1. A house amplifier with an integrated RF gate in the return signal path that is controlled automatically by an automatic detection circuit.
 2. The house amplifier of claim 1 where the gating function eliminates return path ingress noise when the cable modem, eMTA and settop box are not actively transmitting data.
 3. The house amplifier of claim 1 where the automatic detection circuit consists of an RF detector, amplifier, and timing circuit.
 4. The house amplifier of claim 1 where the automatic detection circuit eliminates the need for intervention from a human operator.
 5. The house amplifier of claim 1 where the automatic detection circuit does not interrupt data communications.
 6. The house amplifier of claim 1 where the timing circuit of the automatic detection circuit provides for a delay circuit to prevent ‘early shutoff’ and thus avoid data loss.
 7. The house amplifier of claim 1 where the RF gate can be an RF switch or a voltage controlled variable attenuator.
 8. The house amplifier of claim 1 where the number of RF output ports can vary from 1 to N number of ports.
 9. The house amplifier of claim 1 where the forward path can be amplified or passive pass through.
 10. The house amplifier of claim 1 where the return path can be amplified or passive pass through. 